1. Field of the Invention
This invention is generally concerned with systems and methods for monitoring displays, in particular OLED (Organic Light Emitting Diode) displays.
2. Related Technology
One problem with displays in general, and OLEDs in particular, is unequal aging of pixels of the display. Thus “screen burn” was a feature of cathode ray tube-based monitors of early computer systems. In computers the use of screen savers has reduced the effects of screen burn but, depending upon the application, such techniques are not always applicable. Moreover a particular problem arises in colour OLED displays where pixels of different colors may often age at different rates. In this specification the general term “pixels” is also used to refer to different colored sub-pixels of a colour color display.
One technique for reducing the unevenness in an OLED display is described in WO 2005/069259. This describes an arrangement in which a portable device is monitored by a light sensor in a recharging cradle whilst the device is mounted on the cradle. However this has the disadvantage of requiring a bulky charger which is at least the size of the display. An additional disadvantage is that a separate item of equipment, dedicated to the monitored device, is required.
An alternative approach is described in the applicant's UK Patent Application No. 0408960.3, filed 22 Apr. 2004. This document describes arrangements which incorporate photo sensors into an OLED display, in particular sensing light wave guided in the display substrate. However this has the disadvantage of increasing the manufacturing cost of the display.
Further background prior art can be found in U.S. Pat. No. 6,414,661 and U.S. Pat. No. 5,793,344.